294 
For the Monthly Magazine. 
DISEASES Of TREES. 
HAVE often been surprised that so 
little attention should have been 
given to the subject of diseased vegeta- 
tion, for in the absence of any facts or 
experiments on the origin or progress 
of vegetable life and action, analogy 
alone would warrant us in the conclu- 
sion, that the diseases of plants, like 
those of animals, allow, in the great 
majority of cases, of mitigation, if not 
of actual cure. We are principally in- 
debted to that eminently scientific hor- 
ticulturist Mr. Knight, of Herefordshire, 
for having called the attention of the 
natural philosopher of the last thirty 
vears to the principal phenomena of ve- 
getable life and vegetable disease. The 
sagacity of that gentleman has shewn 
not only that many of our indigenous 
plants were rapidly degenerating, but 
that if attention were not soon paid to 
the subject (so as to produce or raise 
new varieties) several of the best kinds 
of the apple and pear bid fair to become 
quite extinct in England ere another 
generation. 
The value of such inquiry is fully ob- 
vious to every reader of the Monthly 
Magazine; I shall, therefore, offer no 
apology for calling his attention to an 
able report recently made by Mr. Mac- 
leay, at the request of the ranger, Lord 
Sidney, “ On the state of the elm trees 
in St. James’s and Hyde Parks.” The 
object of the inquiry was to ascertain 
the cause of the rapid and increasing 
decay of those venerable elms, and as 
far as possible to suggest some remedy 
for its prevention. 
Mr. M. justly remarks, 
That few persons attribute the cause of 
disease in trees to any other origin than 
one entirely vegetable, or, in other words, 
to the constitution of the plant itself. Yet 
in every case, perhaps, where the disease 
is infectious, and particularly where it is 
confined in a plantation or forest to the in- 
dividuals of one species of tree, we may 
reckon with certainty on its proceeding 
from the attacks of some insect. Every 
tree, and every plant seem to have one or 
more species of insect destined by nature 
to feed on it; and when from the combina- 
tion of various causes (as the weakness of 
vegetation in a particular air or soil, or in- 
attention to the.evil at the proper time for 
effectually checking it) the number of in- 
sects which attack trees, become increased 
beyond certain limits, we must either apply 
the axe without seruple to the seat of the 
disease, or make up our minds to submit 
to the utter destruction of our plantations. 
Almost all the timber-eating insects are 
Diseases of Trees. 
[Nov. 1, 
comprised in three orders, viz. colcoptera, 
or beetles; lepidoptera, or moths and but- 
terflies ; and hymenoptera, or bees, wasps, 
&c.. All these insects, in their early state, 
are worms or larva: and it is while in this 
stage of their life they commit the greatest 
injury to the trees, either by gnawing off 
the bark or devouring the wood. The 
communication of the disease to other trees 
is periodical ; for when those worms arrive 
at their perfect and winged state, the mis-— 
chief committed by them directly is com- 
paratively trifling, and results not so much 
from their voracity as from their attempts 
to extricate themselyes and arrive at the 
external air, or else from their endeavour to 
commit their eggs to a proper nidus. 
But as they are now winged, and capable 
of depositing myriads of eggs, the genus of 
as many devouring larve, the disease is 
thus dispersed throughout, all the neigh- 
bourhood of the tree originally, infected. 
If, however,. it be in this their perfect state 
that these insects are most formidable, hay- 
ing attained the power of propagating the 
disease ; it is also from an accurate know- | 
ledge of them while in this state, that we_ 
can derive any bope of counteracting the 
mischief they-produce. | bees 
Mr. Macleay, after suggesting the ne- 
cessity of studying natural history suffi- 
ciently to make us acquainted with 
these predatory insects in their various 
stages of existence, and the period of 
the year which favours their production 
and dissemivation from tree to tree, 
farther remarks : 
Of the evil which is mentioned aboye, in 
general terms, St. James’s and Hyde Parks 
afford us too many examples. The elm 
trees in both, especially in St. James’s are 
rapidly disappearing, and unless decisive 
measures be soon taken to resist the pro- 
gress of the contagion, we must not only 
expect every tree of this species to be de- 
stroyed in the Parks, but may have to re- 
gret the dissemination of the evil through- 
out all the vicinity of the metropolis. 
In St. James’s Park, which has been 
more particularly under my examination, 
there are several species of beetle to be 
found attacking the elms. That species, _ 
however, which occasions all the havoc 
which we have now to lament, in the Mall 
and Bird Cage Walk, is the hylesinus de- 
structor of Fabricius, or the scolytus destruc- 
tor of Latreille, an insect, of which the his- 
tory is briefly as follows: “ A small beetle, 
with its head rather covered with hair, hav- 
ing a polished black thorax, and brown 
wing-cases ; it- may be seen in great num- 
bers running over the trunks of the elms, 
from the end of March to the beginning of 
July, but chiefly about the end of May or 
commencement of June, It may be seen 
entering into holes in the bark, which have 
the appearance of being perforated with a 
gimblet. It insinuates itself into the cre- 
vices 
